The invention relates to an inductive discharge stabilized switching power supply for electronic apparatus.
Inductive discharge power supplies are known in the art by the name "switched mode", or more commonly "switching", which description will also be used in this case hereinafter.
Power supplies of the switching type are finding ever more frequent use in the supply of electronic apparatus in substitution for those comprising an iron-core transformer with mains frequency and voltage stabilization by means of transistors in series; with respect to those power supplies, those of the switching type operating at high frequencies have a better efficiency, much smaller over-all dimensions and weight and a competitive cost, notwithstanding the greater complexity of circuitry, because of the much smaller incidence of the cost of raw materials such as iron and copper.
Some of the possible solutions for switching power supplies are indicated, for example, in the article "A survey of switched mode power supplies" by L. E. Jansson, in No. 119 of "Mullard technical communications". A number of systems have been proposed which enable the output voltage of switching power supplies to be stabilized by operating on the frequency of repetition of the cycle of storage of the energy in the inductor and of the subsequent discharge to a smoothing capacitor: the frequency of repetition of the cycle is kept low under conditions of high input voltage and of limited output of the power supply; with an increase in the load, and to compensate for lowering of the input voltage, the frequency of repetition of the cycle increases and therefore a greater power is discharged by the inductor to the utilizing circuit.
These stabilizing systems have a number of disadvantages. By lowering the frequency of repetition of the cycle of storage of the energy and of the subsequent discharge, the time of response of the power supply to changes in the load and in the mains supply deteriorates and the problem of filtering the voltage delivered between the succeeding discharges of the inductor, which are more spaced in time from one another, is complicated. Moreover, with these systems, the time of flow of the current in the inductor is constant, so that at each cycle the current in the inductor reaches the maximum value; it is therefore necessary to ensure a consistent safety margin for the maximum value of this current with respect to the saturation current of the inductor. On this account, it is not possible to make the best use of the characteristics of the inductor, of which the energy stored and given up during the discharge is proportional to the square of the maximum current attained.